Metamaterials allow the controlling and tailoring of the optical response of natural materials to achieve unprecedented functionalities. These artificial electromagnetic media can be engineered by structuring on the sub-wavelength scale.
Originally created for achieving extraordinary electromagnetic response (e.g., negative refraction, giant chirality, terahertz magnetism and subwavelength switches) in passive media, metamaterials have been conventionally made out of noble plasmonic metals. As the vast majority of photonic metamaterial architectures today include sub-wavelength metallic resonators arrays, these metamaterial architectures suffer from high energy dissipation due to Ohmic losses, in particular in the near-IR to visible spectral range, which may compromise some applications.
Conversely, all-dielectric resonant metamaterials offer the possibility to alleviate the substantial Ohmic losses while allowing similar functionalities. As the Lorenz-Mie solution to Maxwell's equations reveals, dielectric structures that possess a high refractive index and a size that are comparable or smaller than the wavelength of the incident light support strong optical resonances, known as Mie or leaky-mode resonances. As such, proper control of the resonator geometry and composition allows control of the effective permittivity and permeability of these structures. Due to the absence of Ohmic loss, dielectric metamaterials can be much less absorptive than their metallic counterparts. Recent work has shown that many important attributes of plasmonic metamaterials such as narrow resonances, magnetic response and negative refraction can also be achieved within all-dielectric systems.
Thus far, a wide variety of dielectric metadevice functionalities such as filtering, chirality, broadband reflection, zero index, focusing, as well as optical magnetism, have been demonstrated in silicon and its various alloys as well as high index chalcogenides. Notable applications of such dielectric structures include the realization of strong and tunable light scattering and absorption resonances in nanowires, as well as high efficiency solar cells, photodetectors, resonant nanoantennas, and reconfigurable metasurfaces, predominantly in the near to mid infrared parts of the spectrum.